1. Field of the Invention
The present invention relates to an apparatus for reading and writing information in an IC (Integrated Circuit) card storage and, more particularly, to an IC card reader/writer having a capability of detecting a short-circuit of the IC card circuitry when it is loaded with the card.
2. Description of the Prior Art
An IC card reader/writer capable of detecting a short-circuit between contact pins thereof and ground potential so as to eliminate faults ascribable to the short-circuit has been proposed, as disclosed in Japanese Patent Laid-Open Publication No. 157984/1987 by way of example.
Referring to FIG. 2, a prior art IC card reader/writer with the above capability is shown specifically. As shown, the IC card reader/writer, generally 20, is made up of a card transport section 20A for transporting an IC card 10 into and out of the reader/writer 20, and a read/write section 20B for reading or writing data in the circuitry of the IC card 10 as needed. When the IC card 10 is inserted in the reader/writer 20, the card transport section 20A sets up electrical connection between terminals 13a to 13f of the IC card 10 and contact pins 21a to 21f which are incorporated in the card transport section 20A.
On the insertion of the IC card 10 in the reader/writer 20, the card read/write section 20B checks the terminals 13a to 13f of the IC card 10 for a short-circuit. If the card read/write section 20B does not find any short-circuit, it starts feeding a current to the IC card 10 so as to perform read-out, write-in or similar processing. In this sense, the card read/write section 20B plays the role of a control. The read/writer section 20B has a power source 22 for feeding a current to the IC card 10 as mentioned, a microcomputer 23 for effecting various kinds of control, power source switches 24 and 25, tristate buffers 27-30, a switch driver 31, an AND gate 32, etc. These components of the read/write section 20B are interconnected as shown in FIG. 2.
The AND gate 32 serves to determine whether or not a short-circuit has occurred on the insertion of the IC card 10 in the reader/writer 20. Specifically, the AND gate 32 has five input terminals which are individually connected to the contact pins 21a to 21d and 21f. The output terminal of the AND gate 32 is connected to the control 23. The input terminals of the AND gate 32 and the contact pins 21a to 21d and 21f are individually biased to a predetermined potential by pull-up resistors 31a to 31d and 31f.
In operation, when a power switch, not shown, of the IC card reader/writer 20 is turned on, the microcomputer 23 delivers its output to the switch driver 31 for thereby turning off the power source switches 24 and 25. Then, the tristate buffers 27 to 30 are each brought to a high-impedance state, i.e., an OFF state. In this condition, the reader/writer 20 awaits the insertion of the IC card 10. When the IC card 10 is inserted in the card transport section 20A, its terminals 13a to 13f are individually brought into electrical contact with the contacts 21a to 21f of the card transport section 20A. Thereafter, the microcomputer 23 determines whether the output of the AND gate 32 is in a high level "H" or in a low level "L". Here, the output of the AND gate 32 will be "H" if none of the contact pins 21a to 21d and 21f is short-circuited to the contact pin 21e which is adapted for the ground potential Vss, while it will be "L" if any of the contact pins 21a to 21d and 21f is short-circuited.
When the output of the AND gate 32 is "H", the control 23 turns the power supply switches 24 and 25 to an ON state via the switch driver 31. Then, the control 23 causes the tristate buffers 27 to 30 to switch into an ON state so that data may be read out or written in the IC card 10 via the contact pin 21c and terminal 13c.
On the other hand, when the output of the AND gate 32 is "L", the control 23 executes processing for driving the IC card 10 out of the card reader/writer 20 while maintaining the power source switches 24 and 25 and tristate buffers 27 to 30 in an OFF state. Hence, when the contacts 21a to 21f, especially, the contacts 21d and 21f adapted for power source potential and the contact 21e adapted for ground potential, are short-circuited to each other, the supply of power is interrupted by the power source switches 24 and 25. This is successful in eliminating damage to and malfunction of the card reader/writer 20 and IC card 10. It is to be noted that the short-circuit discussed above will occur when a flat piece of iron or similar conductor is intentionally inserted in the card reader/writer 20 or when impurities are deposited on the contacts 21a to 21f, for example.
The prior art IC card reader/writer 20 has some problems left unsolved, as follows. Generally, the power source Vcc available with the IC card 10 is limited with respect to the allowable range of consumption current Icc, e.g. up to 200 milliamperes as prescribed by ISO (International Organization for Standardization) standards. Hence, assuming that the IC card 10 has a consumption current Icc of 200 milliamperes, the input to the AND gate 32 cannot be guaranteed (i.e., the output of the AND gate 32 cannot be "H" even though a short-circuit to the ground potential Vss is absent) unless the pull-up resistors 31a to 31d and 31f have a resistance as small as about 10 ohms so as to maintain the threshold potential for detection at the AND gate 32 at the transistor-transistor logic (TTL) level. Pull-up resistors 31a to 31d and 31f each having such a high resistance cannot be implemented without using bulky resistors the wattage of which is as high as 2 watts to 3 watts, resulting in an increase in the overall size of the IC card reader/writer 20.
Another problem with the pull-up resistors 31a to 31d and 31f having a low resistance as stated above is that a relatively large current is apt to flow through the contact pins 21a, 21b and 21c also, via their associated pull-up resistors 31a, 31b and 31c. Such a current is liable to disturb data stored in a memory which is built in the IC card 10 and/or to damage a microcomputer which is also built in the card 10.